Phycocyanin in the context of Phycoerythrin

⭐ Core Definition: Phycocyanin

Phycocyanin is a pigment-protein complex from the light-harvesting phycobiliprotein family, along with allophycocyanin and phycoerythrin. It is an accessory pigment to chlorophyll. All phycobiliproteins are water-soluble, so they cannot exist within the membrane like carotenoids can. Instead, phycobiliproteins aggregate to form clusters that adhere to the membrane called phycobilisomes. Phycocyanin is a characteristic light blue color, absorbing orange and red light, particularly 620 nm (depending on which specific type it is), and emits fluorescence at about 650 nm (also depending on which type it is). Allophycocyanin absorbs and emits at longer wavelengths than phycocyanin C or phycocyanin R. Phycocyanins are found in cyanobacteria (also called blue-green algae). Phycobiliproteins have fluorescent properties that are used in immunoassay kits. Phycocyanin is from the Greek phyco meaning "algae" and cyanin is from the English word "cyan", which conventionally means a shade of blue-green (close to "aqua") and is derived from the Greek "kyanos" which means a somewhat different color: "dark blue". The product phycocyanin, produced by Aphanizomenon flos-aquae and Spirulina, is for example used in the food and beverage industry as the natural coloring agent 'Lina Blue' or 'EXBERRY Shade Blue' and is found in sweets and ice cream. In addition, fluorescence detection of phycocyanin pigments in water samples is a useful method to monitor cyanobacteria biomass.

The phycobiliproteins are made of two subunits (alpha and beta) having a protein backbone to which 1–2 linear tetrapyrrole chromophores are covalently bound.

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Phycocyanin in the context of Cyanidiophyceae

Cyanidiophyceae is a class of unicellular red algae within subdivision Cyanidiophytina, and contain a single plastid, one to three mitochondria, a nucleus, a vacuole, and floridean starch. Pyrenoids are absent. Most are extremophiles inhabiting acid hot springs with a pH between 0,2 and 4 and temperatures up to 56 °C. They originated in extreme environments with high temperatures and low pH, which allowed them to occupy ecological niches without any competition.

While still found in extreme environments, they have also adapted to live along streams, in fissures in rock walls and in soil, but usually prefer relatively high temperatures. They have never been found in basic freshwater or seawater habitats. The main photosynthetic pigment is C-phycocyanin. Except for Galdieria partita, which can reproduce sexually, reproduction is asexual by binary fission or formation of endospores. The group, consisting of a single order (Cyanidiales), split off from the other red algae more than a billion years ago. Three families, four genera, and nine species are known, but the total number of species is probably higher. They are primarily photoautotrophic, but heterotrophic and mixotrophic growth also occurs. After the first massive gene loss in the common ancestor of all red algae, where c. 25% of the genes were lost, a second gene loss occurred in the ancestor of Cyanidiophyceae, where an additional 18% of the genes were lost. Since then, some gene gains and minor gene losses have taken place independently in the Cyanidiaceae and Galdieriaceae, leading to genetic diversification between the two groups, with Galdieriaceae occupying more diverse and varied niches in extreme environments than Cyanidiaceae.

View the full Wikipedia page for Cyanidiophyceae

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